High-purity meta-xylene production process

Abstract

There is provided a process for producing high-purity meta-xylene by converting a hydrocarbon feedstream comprising at least about 5 wt % ethylbenzene and at least about 20 wt % meta-xylene, over a single molecular sieve catalyst under ethylbenzene conversion conditions sufficient to provide a primary product stream depleted of more than 50% of the ethylbenzene present in the feedstream. The process can further comprise stripping benzene and/or toluene by-products from the primary product stream to provide a secondary product stream comprising at least about 75 wt % mixed ortho-xylene and meta-xylene; and splitting the secondary product stream by removing substantially all of the ortho-xylene present therein to provide a tertiary product stream comprising at least about 95 wt % meta-xylene.

What is claimed is:  
     
       1. A process for producing purified meta-xylene comprising: 
       converting a hydrocarbon feedstream comprising at least 5 wt. % ethylbenzene, at least 20 wt. % meta-xylene, and less than 5 wt. % para-xylene over a catalyst comprising a single molecular sieve under ethylbenzene conversion conditions sufficient to provide a primary product stream depleted of more than 90% of the ethylbenzene in the feedstream; and  
       stripping benzene and/or toluene by-products from the primary product stream to provide a secondary product stream comprising at least 75 wt. % mixed ortho-xylene and meta-xylene; and  
       splitting the secondary product stream by removing ortho-xylene and heavier materials present therein to provide a tertiary product stream comprising at least about 85 wt. % meta-xylene.  
     
     
       2. A process according to claim  1 , further comprising; 
       distilling the tertiary product stream to obtain a distillate having further increased meta-xylene content.  
     
     
       3. A process according to claim  2 , wherein the distillate comprises at least 98 wt % meta-xylene. 
     
     
       4. A process according to claim  1 , further comprising separating para-xylene from a mixed C 8  hydrocarbon feedstream comprising para-xylene, ortho-xylene, meta-xylene, and ethylbenzene, to provide the meta-xylene-rich feedstream. 
     
     
       5. A process according to claim  1 , further comprising cofeeding benzene with the hydrocarbon feedstream. 
     
     
       6. A process according to claim  1 , wherein the hydrocarbon feedstream comprises from about 5 wt % to about 20 wt % ethylbenzene, from about 20 wt % to about 80 wt % meta-xylene, from about 5 wt % to about 30 wt % ortho-xylene, and from about 0.5 wt % to about 5 wt % para-xylene. 
     
     
       7. A process according to claim  1 , wherein the hydrocarbon feedstream comprises from about 5 wt % to about 20 wt % ethylbenzene, from about 50 wt % to about 65 wt % meta-xylene, from about 20 wt % to about 30 wt % ortho-xylene, and from about 0.5 wt % to about 5 wt % para-xylene. 
     
     
       8. A process according to claim  1 , wherein the ethylbenzene conversion conditions comprise a temperature of from about 200° C. to about 550° C., a pressure of from 0 psig to about 1,000 psig, a WHSV of between about 0.1 hr −1  and about 200 hr −1 , and a H 2 /HC molar ratio of between about 0.2 and about 10. 
     
     
       9. A process according to claim  1 , wherein the ethylbenzene conversion conditions comprise a temperature of from about 325° C. to about 475° C., a pressure of from about 50 psig to about 400 psig, a WHSV of between about 3 hr −1  and about 50 hr −1 , and a H 2 /HC molar ratio of between about 1 and about 5. 
     
     
       10. A process according to claim  1 , wherein the molecular sieve is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-21, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-57, ZSM-58, SAPO-5, SAPO-11, zeolite Beta, zeolite X, zeolite Y, MCM-22, MCM-36, MCM49, and MCM-56. 
     
     
       11. A process according to claim  10 , wherein the molecular sieve is ZSM-5. 
     
     
       12. A process according to claim  1 , wherein the catalyst has been modified by ex situ selectivation, in situ selectivation, coke selectivation, steaming, or a combination thereof. 
     
     
       13. A process according to claim  1 , wherein the catalyst has been modified to include a hydrogenation-dehydrogenation functional metal selected from the group consisting of metals from Groups 3 to 15 of the periodic table. 
     
     
       14. A process according to claim  13 , wherein the catalyst has been modified to include platinum as the hydrogenation-dehydrogenation functional metal. 
     
     
       15. A process according to claim  13 , wherein the catalyst has been modified to include rhenium as the hydrogenation-dehydrogenation functional metal. 
     
     
       16. A process according to claim  1 , wherein the catalyst has an ortho-xylene t 0.3  sorption time of greater than about 50 min at 4.5±0.8 mm Hg and 120° C. 
     
     
       17. A process according to claim  1 , wherein the catalyst produces less than 12 wt % para-xylene when contacting a feed containing 60 wt % meta-xylene, 20 wt % ortho-xylene, and 20 wt % ethylbenzene at a temperature of 426.7° C, a pressure of 150 psig, a WHSV of 20 hr −1 , and a H 2 /HC molar ratio of 1. 
     
     
       18. A process for production of purified meta-xylene from a mixed C 8  aromatic feedstream, comprising: 
       separating para-xylene from a mixed C 8  hydrocarbon fluid comprising para-xylene, ortho-xylene, meta-xylene, and ethylbenzene, to provide a hydrocarbon feedstream comprising at least 5 wt % ethylbenzene, at least 20 wt % meta-xylene, and less than 5 wt % para-xylene;  
       converting the hydrocarbon feedstream over a catalyst comprising a single molecular sieve under ethylbenzene conversion conditions sufficient to provide a primary product stream depleted of more than 50% of the ethylbenzene present in the feedstream;  
       stripping benzene and/or toluene by-products from the primary product stream to provide a secondary product stream comprising at least 75 wt % mixed ortho-xylene and meta-xylene; and  
       splitting the secondary product stream by removing orthoxylene and heavier materials present therein to provide a tertiary product stream comprising at least 95 wt % meta-xylene.